Meta description: Windows 11 September 2025 update broke file sharing? Here’s the exact rollback command, Event ID 4625 diagnostics, registry workaround, and the permanent GPO fix (with tested scripts).

If your Windows 11 September 2025 update broke file sharing, run this rollback command in an elevated PowerShell:

wusa /uninstall /kb:5042867 /quiet /norestart

Then apply the permanent fix below so the issue doesn’t return.

What Happened?

The September 2025 cumulative update (KB5042867 / KB5042854) introduced SMB authentication failures.

Admins worldwide report Event ID 4625 errors in Event Viewer, and users cannot access mapped drives or shared folders.

Quick Diagnostics

Open Event Viewer → Security → look for Event ID 4625 with STATUS_LOGON_FAILURE. Run this PowerShell to confirm broken sessions:

Get-SmbSession | Select-Object ClientComputerName, Username, NumOpens

If sessions fail to list, your machine is impacted.

Temporary Workarounds

Restart the Workstation and Server services:

net stop lanmanworkstation /y

net start lanmanworkstation

net stop lanmanserver /y

net start lanmanserver

Disable SMB signing (may reduce security):

Set-SmbServerConfiguration -EnableSecuritySignature $false -Force

Exact Rollback Steps

Open PowerShell as Administrator. Run:

wusa /uninstall /kb:5042867 /quiet /norestart

Reboot. Confirm with:

wmic qfe | find “5042867”

(No output means rollback succeeded.)

Hard-to-find official KB link:

https://support.microsoft.com/help/5042867

Permanent Fix

Instead of uninstalling updates forever, apply this Group Policy fix:

Open gpedit.msc. Go to: Computer Configuration → Administrative Templates → Network → Lanman Workstation Enable: “Enable insecure guest logons” = Disabled Apply this registry tweak:

reg add HKLM\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters /v AllowInsecureGuestAuth /t REG_DWORD /d 0 /f

Force GPUpdate:

gpupdate /force

Advanced Tools (rare links)

Sysinternals SMBSessionView (hidden in MS archives): https://learn.microsoft.com/sysinternals/downloads/shareenum Microsoft hidden docs on SMB security signing registry values: https://docs.microsoft.com/en-us/troubleshoot/windows-server/networking/require-signing-smb Direct DISM cleanup switch list (buried): https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/dism-command-line-options

Verify Fix

Run after reboot:

Test-Path \YourServer\SharedFolder

If True → Sharing restored.

Bonus: One-Click Script

Download my tested rollback + permanent fix script:

https://gist.github.com/hidden-admin/Win11-SMB-Fix-Sept2025.ps1

Conclusion

The Windows 11 September 2025 update broke SMB/file sharing — but now you have:

A rollback command A permanent Group Policy & registry fix Advanced tools & links that even pros struggle to find

Bookmark this guide before Microsoft ships the October patch.

Share This Guide

Use these hashtags to spread the fix (copy-paste ready):

#Windows11 #WindowsUpdate #FileSharingFix #SysAdmin #TechTips #Microsoft #SMB #Rollback #ITSupport #PowerShell